1. Field of the Invention
The present invention relates to apparatus and methods for activating electric wireline firing systems in which a firing pin is actuated by pressure, and more particularly, to such apparatus and methods in which the firing pin is not actuated simultaneously with application of electrical voltage to the apparatus.
2. Description of Related Art
Many devices conventionally utilized to complete or work over a subterranean well, such as perforating guns, jet cutters, and chemical cutters, are actuated by applying electrical current of a specified voltage to an electric detonator via a wireline on which the device is suspended from a surface wellhead. Application of the specified electrical voltage via wireline to these devices detonates an electrical blasting cap or detonator which is connected to and in turn detonates the explosive charge of a perforating gun, a jet cutter, a chemical cutter, or a similar system. The electrical current required to detonate the blasting cap or detonator of these devices is relatively low, for example 0.2 amps for a duration of one second or less.
A significant problem associated with detonating such conventional devices via an electric wireline is that the presence of high radio frequencies, stray voltages, or other electrical influences, such as welding or cathodic protection, in the vicinity of the surface location of the wellhead may inadvertently result, via an electrical short in the wireline spool or if the device is not properly grounded, in the premature detonation of the device at the surface or prior to proper placement of the device at a desired location within a subterranean well. Premature detonation can also result from human error of inadvertent supplying sufficient electrical voltage to detonate the firing apparatus. Such premature detonation results in an extremely unsafe operating environment which can result in injuries and even fatalities at or near the wellhead. It is believed that the majority of accidents involving the use of explosives in a subterranean well are a result of such premature detonations.
In an effort to improve the safety of detonation operations using an electric wireline, operators have attempted to eliminate radio frequencies and stray voltages near the wellhead. However, such operations can take a considerable amount of time and be expensive and have not been completely effective, especially in more populous areas where complete elimination of radio frequencies, stray voltages and other electrical influences generated by third parties is often not practical. Thus, a need exists for an electric wireline firing system which can be safely used in conjunction with a conventional downhole explosive device.
Accordingly, it is an object of the present invention to provide a method and apparatus for safely activating electric wireline firing systems.
It is another object of the present invention to provide a method and apparatus in which the firing pin of an electric wireline firing system is not actuated simultaneously with application of electrical voltage to the apparatus.
It is a further object of the present invention to provide a method and apparatus for safely activating the firing pin of an electric wireline firing system which is inexpensive to construct and to operate.
it is a still further object of the present invention to provide a method and apparatus for safely activating the firing pin of an electric wireline firing system which requires that a relatively high voltage be applied to detonate the firing apparatus.